The present capability of gun fire-control systems for point defense against antiship missiles is limited by normal gun system errors and the number of projectiles that can be fired during a short engagement. For this reason guided missiles are used as a defense against antiship missiles. However, the effectiveness of such guided missiles is limited to a minimum range of several miles. Furthermore, they can be used only on specially equipped missile ships. The employment of antiship missile systems aboard a ship requires that major and expensive modifications be made to the ship or that the ship be particularly designed for the missiles.
Guided spinning shells have been conceived to alleviate some of these problems. However because they are not compatible with existing shipboard guns they also require major ship modifications. Also, the guidance system for such spinning shells have been of the pursuit course navigation type which has proved ineffective against moving targets. Pursuit course navigation requires for major corrections in ballistic path to be made in the latter part of the flight, at a time when maximum lift necessary to make the correction is often not available.